The Confounding Effect of River Discharge on Estuarine Response to Nutrient Loading

Borsuk, M. E., C. A. Stow, and K. H. Reckhow. 2004. Confounding effect of flow on estuarine response to nitrogen loading. Journal of Environmental Engineering, 130: 605-614.

Craig A. StowNOAA Great Lakes Environmental Research Laboratory

Ann Arbor, MI

Additional Insights and Inputs provided by Conrad Lamon and Song Qian

The Neuse River Basin

Courtesy USGS

Vollenweider Cross-Sectional Lake Nutrient Loading Model

Brazenly stolen from:Vollenweider, R.A. 1976. Advances in defining critical loading levels for phosphorus in lake eutrophication. Mem. Ist. Ital. Idrobiol., 33:53-83.

Single Lake Relationship:

Positive

Negative

Nonlinear

River Flow

Nutrient Loading

Nutrient Concentration Eutrophication

EstimatedNutrient Loading

EstimatedConcentration=

f(Flow)

Residence TimeTurbiditySalinity

Temperature

River discharge highly variable – even on relatively long time-scales

Drives Nutrient Load Variability at this scale

Concentration:Flow relationships idiosyncratic: positive, negative, or non-monotonic

In the Neuse the relationship was negative

-9

-8

-7

-6

-5

12 13 14 15 16 17 18

Log flow

Log

conc

entra

tion

Data Provided by:NC DENR DWQ – nutrient concentrationsUSGS – daily flow

High load = low concentrations

New New BernBern

10 miles

10 kilometers

10

20

30

40

50

0

6070

8090

100110

120 130140

150160

170

180

N

Water Quality StationWater Quality Station

Hydrographic StationHydrographic Station

River

Upper

Middle

BendLower

Upper

Middle

Bend

Model SectionsModel Sections

chlTNT

wey

TNTflowIflow

flowIflowchl

)()20(}){ln(}){ln(

}){ln(}){ln()ln(

sec,secsecsec,2

secsecsec,1sec,0

Chlorophyll a Model(Bayesian multilevel piecewise lognormal model)

Med

ian

Ann

ual T

otal

N (m

g/L)

0.25

0.50

0.75

1.00

1.25

1.50

1.75

Fort Barnwell Total N Load (tonnes)

2000 3000 4000 5000 6000 7000

Ft. BarnwellSwift CreekNew BernBroad CreekOrientalPamlico

Estuarine N Concentrations vs. Annual N Load

Med

ian

Ann

ual T

otal

P (m

g/L)

0.02

0.12

0.22

0.32

0.42

Fort Barnwell Total P Load (tonnes)

300 400 500 600 700 800 900 1000 1100 1200 1300

Ft. BarnwellSwift CreekNew BernBroad CreekOrientalPamlico

Estuarine P Concentrations vs. Annual P Load

Summary

Nonlinear chlorophyll, flow (~ load) relationship on short time-scales

Relationship differs systematically along spatial gradient

Maximum differs systematically along spatial gradient

No relationship between nutrient load, concentration on medium time-scales

This may differ among systems

Nutrient Loading

Eutrophication

Hypoxia

Nutrient Loading

TMDLs

Eutrophication

Hypoxia

Nutrient load targets appropriate on longer (multi-year) time scales

Short-term (yearly or less) misleading

Assuming stationary flow (long-term)

Year

Log

Flow

1980 2000

-0.3-0.2-0.10.00.10.2

Jan

1980 2000

Feb

1980 2000

Mar

1980 2000

Apr

1980 2000

May

1980 2000

Jun

1980 2000

Jul

1980 2000

Aug

1980 2000

Sep

1980 2000

Oct

1980 2000

Nov

1980 2000

Dec

1980 1985 1990 1995 2000 2005

5.5

5.65.75.8

Log

Flow

1980 1990 2000

-0.2

0.0

0.2

Trend

1980 1990 2000

Seasonality

1980 1990 2000

Residuals

Mississippi River Flow – Seasonal Trend Decomposition Using Loess

April 2006 - U.S. Court of Appeals District of Columbia Circuit ruled that EPA-approved plan to limit pollution into Anacostia River contrary to Clean Water Act requirements to set "total maximum daily loads" of pollutants.

January 2007 -- United States Supreme Court let stand lower court ruling requiring limits on pollution allowed in Anacostia River each day. 

                             

Anacostia River in Washington, DC

Photo by City of Washington DC

River Flow

Nutrient Loading

Nutrient Concentration Eutrophication

Upper Trophic LevelEffects

Hypoxia?

The End

River Flow

Nutrient Loading

Hypoxia

EstimatedNutrient Loading